1. Field of the Invention
The present invention relates generally to sonar, and particularly to a system and method for processing active sonar return signals.
2. Technical Background
Active sonar refers to sonar systems that employ radiating acoustic sources to search for one or more submerged objects. Conventional sonar systems may be configured to direct a highly directional beam of sonic energy on a periodic basis. All sonar systems include a receiver that is configured to detect echoes reflected from any object(s) within the propagation channel.
Sonar devices tend to experience high transmission losses which increase as a function of the frequency of the propagated energy. Active sonar return signal propagation is affected by the channel and/or the characteristics of the target. Signal distortion in an active sonar system may occur for various reasons. For example, irregular sea bottoms and surface interactions may cause distortion. Distortion may also be caused by nonlinear resonant scattering within the propagation channel, reverberation, non-homogenous responses due to channel and/or target interactions, target scattering profiles, multi-path reflections, noise generated by waves, transmission losses, and/or changing distances from the target.
On the other hand, sonar receivers typically do not fully utilize the phase or phase difference information contained within the received waveform when processing active sonar return signals. Return signal data is often processed by evaluating target amplitude. Any phase information that may have been present is not processed, and is therefore lost. This approach to processing sonar return signals may result in target detection when the target amplitude is above the background noise or reverberation. However, when the amplitude of a return is less than or approximately equal to than the background noise, a receiver employing simple detection and thresholding techniques may not extract the target of interest.
What is needed is a system that is configured to use the phase information in the sonar return signal. In particular, what is needed is a sonar receiver that processes the phase of the target of interest to distinguish the target from the background phase.